Non-fibrous cellulosic food casings containing about 20 wt.% of total plasticizer based upon the bone dry weight of cellulose in the casings are known in the prior art. By way of illustration, O'Brien U.S. Pat. No. 4,163,463 discloses non-fibrous shirred casings having a glycerine content of between 15 wt.% and 20 wt.% on a moisture-free basis, which is equivalent to between about 18 wt.% and about 25 wt.% based on the bone dry weight of cellulose in the casing, and a moisture content of 10 to 15 wt.% based upon total casing weight, which is equivalent to from about 12 to about 20 wt.% based upon the bone dry weight of cellulose in the casing. The glycerine is used in this patent as a plasticizer for the casing.
The O'Brien '463 patent also discloses in column 7, lines 19 to 21 thereof that the conventional glycerine level may be cut in half for non-fibrous, shirred casing when a supplemental oxazoline wax plasticizer is also employed. O'Brien teaches that the oxazoline wax plasticizer must be added to the viscose with an emulsifier so that the wax plasticizer is thoroughly dispersed when the viscose is regenerated into cellulose.
Hammer et al U.S. Pat. No. 4,198,325 discloses a required primary alkyl derivative plasticizer in combination with an optional secondary plasticizer (e.g. a polyol) in cellulosic fibrous food casing. The primary plasticizer is broadly disclosed as being present in an amount of between about 0.5 and about 40 wt.% of the amount of cellulose in the fibrous casing, preferably between about 5 and about 20% by weight of the cellulose in the casing (column 10 of Hammer). However, the illustrative examples given at columns 8 and 9 of Hammer all contain total plasticizer levels (items 2 and 5 of the examples) that calculate to be above 20 wt.% of the bone dry weight of cellulose in the casing.
Shirred cellulosic fibrous food casings having very low total plasticizer levels and very high moisture levels have been disclosed in the art. For example, German patent publication DE3220488A1 discloses shirred, cellulosic casing having 0 wt.% to 40 wt.%, and preferably having 10 wt.% to 35 wt.% of glycerine plasticizer and having 35 to 80 wt.% of moisture, all wt.% values being based upon the weight of the bone dry cellulose in the casing.
As an additional illustration, Bridgeford Canadian Pat. No. 1,180,939 discloses shirred non-fibrous cellulosic frankfurter casings containing a glycerine plasticizer in an amount of from 0 wt.% to 10 wt.% based upon the dry weight of cellulose in the casing.
It must be noted that in certain respects nonfibrous cellulosic casing and fibrous cellulosic casing are nonanalogous. Nonfibrous casing derives its strength and performance properties solely from the molecular interaction of the regenerated cellulose molecules. In contrast, fibrous casing derives its strength from both the fiber structure of the paper web substrate as well as the fiber-to-cellulose molecular bonding, and it thereby achieves strength which is superior to the inherent strength of either the fibrous paper web alone or the regenerated cellulose alone.
This invention relates to flat stock cellulosic casing as distinguished from shirred cellulosic casing. In a preferred embodiment the invention relates to cut flat stock cellulosic casing and, as used herein, "cut" refers to flat stock casing which, when mounted on the horn of the stuffing machine, has a total length not exceeding about 100 inches. The cutting may be done by the casing manufacturer prior to sale, or the casing may be sold in the reel form and later be cut by the food processor or an agent of the food processor.
Heretofore, to the best of our knowledge, flat stock cellulosic fibrous food casings, having a total plasticizer content below 20 wt.% based on the bone dry weight of cellulose in the casing, have not been commercially used. Commercial flat stock cellulosic fibrous casing has conventionally employed about 30 wt.% of total plasticizer (e.g., polyol) based upon the bone dry cellulose weight. It is speculated that there is an important technical reason why such a high level of total plasticizer, e.g. 30 wt.% based upon bone dry cellulose weight, has been conventionally employed as the plasticizer in flat stock casing. Because conventional commercial flat stock fibrous casing has a moisture level of only about 6 to 10 wt.% based upon bone dry cellulose, in contrast to conventional commercial shirred fibrous casing which has a typical moisture level of 30 to 50 wt.% based upon bone dry cellulose, flat stock fibrous casing is very brittle and easily damaged. Since flat stock fibrous casings must be subjected to several processing and handling operations before stuffing the casing with food product, including cutting, pre-sticking, and tying operations, heretofore the industry has believed that only by maintaining a high total plasticizer level of about 30 wt.% will the low moisture flat stock fibrous casing be able to withstand the rigors of these processing operations. In addition to acting as a plasticizer for the flat stock fibrous casing, it was believed that a high plasticizer (e.g., polyol) level was needed as a humectant, so that moisture loss would be minimized prior to these processing steps. Thus, only high plasticizer (e.g., glycerine) levels have been commercially used in flat stock fibrous cellulosic casing, despite the fact that plasticizers such as glycerine are expensive and that lower plasticizer levels would result in casing production cost savings.